The present invention relates to devices known variously as traversing machines, positioning devices, actuators, etc. More particularly, the invention relates to such devices with the ability to traverse along more than a single axis.
A two-axis motor with a stage (also known as a forcer) supported by an air bearing on a motor platen surface is described in U.S. Pat. No. 5,334,892, the entirety of which is incorporated herein by reference. In this motor, the motor platen has a rectangular array of permanent magnets embedded in it. Mutually perpendicular sets of X and Y coils in the stage interact with the magnetic fields of the magnets to move and position the stage.
In the prior art motor described above, the packing density of the magnets in the motor platen is about 50%. It is desirable to increase the magnetic flux density to increase the peak motive force on the stage and also to allow a larger air gap between the stage coils and the platen magnets. Cogging is also an ever-present problem in such motors.